You Do Not Have Diabetes Insipidus
Based on your laboratory results, you definitively do not have diabetes insipidus. Your urine osmolality of 498 mOsm/kg demonstrates excellent renal concentrating ability, which is the opposite of what occurs in diabetes insipidus 1.
Why Your Results Rule Out Diabetes Insipidus
Diagnostic Criteria Not Met
The diagnosis of diabetes insipidus requires three key findings occurring simultaneously 2, 1:
- Inappropriately dilute urine (osmolality <200 mOsm/kg)
- High-normal or elevated serum sodium (>145 mEq/L with restricted water access)
- Polyuria (>3 liters per 24 hours in adults)
Your results show the exact opposite pattern:
Your urine osmolality is 498 mOsm/kg - This is highly concentrated urine, demonstrating that your kidneys are responding perfectly to antidiuretic hormone (ADH) and concentrating urine appropriately 1. Diabetes insipidus requires urine osmolality definitively <200 mOsm/kg 2.
Your serum sodium is 143 mEq/L - This is completely normal, not elevated 2. While you mentioned "hypernatremia" in your question, a sodium of 143 is within the normal range (135-145 mEq/L).
Your copeptin level is 4.6 pmol/L - This is actually a low-normal level, not elevated 3, 4. In nephrogenic diabetes insipidus, baseline copeptin levels would be >21.4 pmol/L, indicating the kidneys are not responding to very high ADH levels 3, 2, 1, 5.
Understanding Your Copeptin Level
Your copeptin of 4.6 pmol/L after a 12-hour fast is within the normal range and does not suggest diabetes insipidus 4, 5:
- Nephrogenic diabetes insipidus requires baseline copeptin >21.4 pmol/L without any stimulation test 3, 2, 5
- Central diabetes insipidus would show copeptin <4.9 pmol/L even after osmotic stimulation (when serum sodium reaches >147 mEq/L) 5, 6
- Your level of 4.6 pmol/L after mild overnight fasting is entirely normal and indicates appropriate ADH secretion and kidney response 4
Your Kidney Function is Normal
The combination of your results demonstrates normal kidney concentrating ability 1:
- Urine osmolality 498 mOsm/kg with serum osmolality 301 mOsm/kg gives a urine-to-serum osmolality ratio of 1.65, which is excellent
- This ratio should be >1.0 in normal kidney function, and yours exceeds this significantly 2
- Your other electrolytes (calcium 9.8, uric acid 5.4, chloride 103, CO2 25) are all normal and do not suggest any disorder of water balance 2
What Could Explain Your Symptoms
If you're experiencing increased thirst or urinary frequency, consider these alternative explanations 1:
Anxiety-Related Polydipsia
- Excessive fluid intake driven by anxiety or habit can cause urinary frequency 1
- Your kidneys are appropriately producing concentrated urine when given the opportunity (as shown by your 498 mOsm/kg result) 1
- Management: Address underlying anxiety, drink to thirst rather than habit, and avoid excessive fluid intake 1
Overactive Bladder or Urological Causes
- Urinary frequency without true polyuria (>3 liters/24 hours) suggests bladder dysfunction rather than diabetes insipidus 1
- Consider evaluation by a urologist if frequency persists 1
Diabetes Mellitus (Must Be Ruled Out First)
- Check fasting blood glucose to rule out diabetes mellitus, which causes polyuria through osmotic diuresis from glucosuria, not ADH deficiency 2
- Diabetes mellitus would show high urine osmolality (from glucose), hyperglycemia, and glucosuria 3, 2
Critical Distinction
Many conditions can cause urine osmolality in the 200-300 mOsm/kg range without representing true diabetes insipidus 2. However, your urine osmolality of 498 mOsm/kg is far above even this intermediate range and definitively excludes diabetes insipidus 2, 1.
The diagnosis of diabetes insipidus requires urine osmolality definitively <200 mOsm/kg in the setting of serum hyperosmolality, and a water deprivation test followed by desmopressin administration remains the gold standard for diagnosis when results are equivocal 2. Your results are not equivocal—they clearly exclude diabetes insipidus 1.